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WAEC Further Mathematics 2010 Question 9

Question 9

Trigonometry

If sin x = −sin 70°, 0° < x < 360°, determine the two possible values of x.

  1. A.110°, 250°
  2. B.110°, 290°
  3. C.200°, 250°
  4. D.250°, 290°
Show the answer and explanation

Answer: D (250°, 290°)

Explanation

sin x is negative in the 3rd and 4th quadrants with reference angle 70°: x = 180° + 70° = 250° or x = 360° − 70° = 290°.